Assembly including plural through wafer vias, method of cooling the assembly and method of fabricating the assembly

ABSTRACT

An assembly includes a chip including an integrated circuit, a casing including an integrated circuit and having an upper portion formed on a side of the chip and lower portion formed on another side of the chip, plural through-wafer vias (TWVs) for electrically connecting the integrated circuit of the chip and the integrated circuit of the casing, and a card connected to the casing for electrically connecting the casing to a system board.

RELATED APPLICATIONS

The present application is a Divisional application of U.S. patentapplication Ser. No. 11/933,107 which was filed on Oct. 31, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an assembly including pluralthrough wafer vias and more particularly, an assembly including throughwafer vias that electrically connect an integrated circuit of a chip andan integrated circuit of a casing having upper and lower portions formedon a side of the chip.

2. Description of the Related Art

Commercially available cold plates for single and multi-chipapplications are designed for uniform heat removal. However, the powerdissipation of an IC-chip is strongly non-uniform. A cold plate designedfor uniform heat flux with the maximal power density as design point isnot economical, since its heat removal capability at cache locations isexceeding the needs and results in waste of pumping power and loss ofenergy. These problems get accentuated in 3D stacked chips since thespace for fluid manifolding and for heat removal is constrained.

A related art method for providing heat dissipation in 3D stacked chipsintersperses specialized cooling structures at periodic points withinthe monolithic structure of the chip stack. In this related art method,a special pair of chips is interspersed. One chip has had a trenchetched into it, and the other acts as a cap. When the chips are puttogether and interspersed between active chips, the chips form coolingchannels.

C-4 bumps provide electrical connection to the individual chips on oneface of the structure, while the cooling channels are exposed on asecond face. A fluid manifold is attached to the second face to providecoolant flow. The trenches may be etched in the cooling channels. Morethan one face may be used for electrical connection to the chip stack.

In another embodiment of this related art method, metal cooling platesof Aluminum, Copper, Molybdenum, etc. are interspersed between activechips. The C-4 bumps provide electrical connection to the individualchips on one side of the face of the structure, while the cooling platesare connected to a heat sink on a second face. More than one face maycontain electrical connection to the chip stack.

However, in this related art method, the cap chip and trench chips arenot active chips. Thus, this related art method is an inefficient use ofspace on the system board.

SUMMARY OF THE INVENTION

In view of the foregoing and other exemplary problems, drawbacks, anddisadvantages of the conventional methods and structures, an object ofthe present invention is to provide an assembly that may result in amore efficient use of space on the system board than in conventionalstructures.

An exemplary aspect of the present invention is directed to an assemblywhich includes a chip including an integrated circuit, a casingincluding an integrated circuit and having an upper portion formed on aside of the chip and lower portion formed on another side of the chip,plural through-wafer vias (TWVs) for electrically connecting theintegrated circuit of the chip and the integrated circuit of the casing,and a card connected to the casing for electrically connecting thecasing to a system board.

Another exemplary aspect of the present invention is directed to amethod of cooling a chip stack in an assembly. The method includestransporting a coolant fluid to the chip stack through an inlet formedin a casing, the casing including an integrated circuit which iselectrically connected to an integrated circuit of a chip in the chipstack by plural through wafer vias, transporting the coolant fluid in afluid channel formed between chips in the chip stack, and transportingthe coolant fluid from the chip stack through an outlet formed in acasing.

Another exemplary aspect of the present invention is directed to amethod of forming an assembly. The method includes providing a chipincluding an integrated circuit, forming a casing including anintegrated circuit, an upper portion of the casing being formed on aside of the chip and a lower portion of the casing being formed onanother side of the chip, forming plural through-wafer vias (TWVs) forelectrically connecting the integrated circuit of the chip and theintegrated circuit of the casing, and connecting a card to the casingfor electrically connecting the casing to a system board.

With its unique and novel features, the exemplary aspects of the presentinvention may provide an assembly which may result in a more efficientuse of space on the system board than in conventional structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other exemplary purposes, aspects and advantages willbe better understood from the following detailed description of anexemplary embodiment of the invention with reference to the drawings, inwhich:

FIG. 1 a illustrates an input/output assembly 100 according to anexemplary aspect of the present invention;

FIG. 1 b illustrates rows 135 of solder balls on the upper casing 111alternately formed with the rows 136 of solder balls on the lower casing112, according to an exemplary aspect of the present invention;

FIG. 2 illustrates an assembly which may be used for chip identificationpersonalization, according to an exemplary aspect of the presentinvention;

FIG. 3 illustrates an assembly which may be used for multiple signal useof the same Z coordinate, according to an exemplary aspect of thepresent invention;

FIG. 4 illustrates an assembly that may be used for a sensor applicationand/or emitter application, according to an exemplary aspect of thepresent invention;

FIG. 5 illustrates another assembly, according to an exemplary aspect ofthe present invention;

FIG. 6 illustrates a cross-section of a through-wafer via 123, accordingto an exemplary aspect of the present invention;

FIG. 7 illustrates an assembly 700 according to another exemplary aspectof the present invention;

FIG. 8 illustrates an assembly 800 according to another exemplary aspectof the present invention;

FIG. 9 provides an isometric view of a cross-section of an assembly 900according to an exemplary aspect of the present invention;

FIG. 10 illustrates a method 1000 of cooling a chip stack in anassembly, according to an exemplary aspect of the present invention; and

FIG. 11 illustrates a method 1100 of fabricating an assembly, accordingto an exemplary aspect of the present invention; and

FIGS. 12A-12C illustrate assemblies 1200, 1300 and 1400, respectively,according to other exemplary aspects of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring now to the drawings, and more particularly to FIGS. 1 a-12C,there are shown exemplary embodiments of the method and structures ofthe present invention.

Overview

Conventional cold plates cannot optimally remove heat from chips (e.g.,processor chips) since they are attached via a thick chip, a thermalinterface, and a cooler bottom plate. All these components spread theheat from hotspots laterally and the heat is transferred to the liquidusing a uniform heat transfer coefficient. This approach is not optimalin terms of pumping energy efficiency and entropy. In the constrainedspace between two active chips, these problems are accentuated and needto be solved to reach acceptable performances. The geometricalconstraint combined with the high density of area array verticalinterconnects cause a high fluid resistance. The result is a low massflow rate of coolant for a given pressure drop from inlet to outlet. Forexample, a uniform heat transfer with a 150 micron gap and a 200 microninterconnect pitch allows only the removal of ˜70 W/cm².

The present invention, on the other hand, provides a structure that mayindividually and in combination result in an improved cold plateefficiency. First, the invention may redistribute hot spots tothermodynamically efficient locations (e.g. at fluid inlets), where thefluid temperature is still low. Second, the invention may remove orchange the density distribution of interconnects to reduce the fluidresistance to the hot spot providing sufficient interconnects for localand global needs. Third, the invention may manifold the fluid withguiding structures to the hot spot for an increase in local flow ratealso including delivery and drainage of coolant from plural (e.g., four)sides. This multi-port (e.g., four-port) cold plate architecture resultsin shorter fluid paths for handling of hotspots.

In addition, fluid flow may be directed such that for a given power mapa uniform junction temperature of T_(max) and a minimal pumping power isreached. The increased fluid outlet temperature can eliminate thesecondary cooling loop by direct exchange of the heat to the ambient.The heat transfer geometry is structured into silicon to form fins thatmatch the through silicon via-holes. The selected packaging approachreduces stress from thermal expansion mismatch and allows two sided heatremoval for all dies.

The combination of all the above mentioned features results in amulti-port locally adapted heat removal geometry for an optimal amountof electrical interconnects. The geometry may be designed for a hot spotoptimized power map resulting in a uniform junction temperature. Unlikeconventional structures in which power density limits force the circuitdesigner to spread the hot spots over the chip surface, in the claimedinvention, it may be energetically beneficial to cool optimal locatedhot spots. This typically allows removal of 2× larger overall power froma chip and up to 4× higher hotspot power densities than a uniformcooling approach.

DETAILED DISCUSSION

In certain applications of 3D Integration technology, a highest possiblebandwidth as well as a minimum signal latency is important forsustaining high-throughput. The problem is that this bandwidth andlatency advantage is squandered if it is not propagated out onto thesystem board. The scaling of conventional chip packaging technology hasnot kept up with chip-level integration interconnect density.

The present invention allows the chip packaging to more closely matchthe chip integration interconnect density.

It is projected that thru-wafer vias (TWVs) (e.g., 3D-Integrated TWVs)in chip stacks may potentially become smaller than 1 micron in diameter.Packaging technology interconnections such as C-4 presently has becomelimited to 3 millimeter diameter balls on 6 millimeter centers, which is3 decades largers that the 3D Integrated pitch.

The present invention includes an improved packaging technology thatuses TWVs which run through a chip stack and contact adjoining C-4solder joints on one side or the other of the stack. For example, in oneexemplary aspect, the TWVs run completely through a chip stack andcontact adjoining C-4 solder joints alternately on one side or the otherof the stack, thus interleaving I/O above and below the stack.

The challenge then is that the heatsink, which in conventionalstructures is typically mounted on one side or the other of the stack tokeep the part within reliability temperature limits, is now displaced bysignal I/O, and a new cooling method must be substituted.

In the present invention, the conventional heatsink may be replaced byusing a cooling fluid at areas of high power dissipation density. In anexemplary aspect of the present invention, microfluidic or gas coolingchannels may be etched within the chip stack, to help transport thecooling fluid to areas of high power dissipation density.

FIG. 1 a illustrates an input/output assembly 100 according to anexemplary aspect of the present invention. As illustrated FIG. 1 a, theassembly 100 may include a chip stack 110.

The chips 110 a-110 c in the chip stack 110 may have integrated circuits150 a-150 c including active elements (e.g., transistors, diodes,resistors, etc.) formed thereon, respectively. For example, theintegrated circuits 150 a-150 c may include microprocessor circuitsincluding plural logic elements. The chips (e.g., layers) of the chipstack 110 may be interconnected by using TWVs 123. That is, the TWVs 123may electrically interconnect the active elements on the chips in thestack 110.

The chips in the stack 110 may include, for example, a microprocessorelement formed thereon. It should be noted that although FIG. 1 aillustrates a chip stack 110 including three chips, the chip stack 110may include one or more chips.

The assembly 100 may also include circuitboards 115 which include wiring116 (e.g., “circuitboard wiring”) for porting the signals to a systemboard 120, via connectors 121 formed on the system board 120. The chipstack 110 may be connected to upper casing 111 and lower casing 112 byplural vertical vias 125. Importantly, the upper casing 111 and lowercasing 112 may include integrated circuits 117 a, 117 b which areelectrically connected to the integrated circuits 150 a-150 c in thechip stack by the TWVs 123.

Plural C-4 solder balls 130 may be used to bond and electrically connectthe casings 111, 112 to the daughercards 115. The C-4 solder balls 130may be formed in an array of rows and columns on both the upper andlower casings 111, 112. Further, the rows and/or columns of solder balls130 may be alternately formed on the upper and lower casings 111, 112 sothat I/O is interleaved above and below the stack. For example, FIG. 1 aillustrates an example of where a row of solder balls 130 on the uppercasing 111 is interleaved with a corresponding row of solder balls 130on the lower casing 112, so that the larger solderballs may fit in thetighter pitch of the through-silicon vias.

It should also be noted that entire rows and/or columns of solder balls130 in the solder ball arrays on the upper and lower casings 111, 112may be alternately formed. For example, as illustrated in the plan viewof FIG. 1 b, the rows 135 of solder balls on the upper casing 111 arealternately formed with the rows 136 of solder balls on the lower casing112.

It is important to point out that like the chips in the stack 110, theupper and lower casings 111, 112 may include active elements (e.g.,transistors, diodes, resistors, etc.) formed thereon. That is, thevertical vias 125 may be used to electrically connect the activeelements formed on the upper and lower casings 111, 112 to stack 110 andthe Circuit boards 115. Thus, the 3D integrated circuit of the presentinvention may include not only the active elements on the chips of thechip stack 110, but also the active elements on the casings 111, 112.This may allow the present invention to achieve a more efficient use ofspace than in conventional structures.

Coming out of the chip stack 110, the plural vertical vias 125 (e.g.,many thousands of vertical vias, ostensibly having a diameter of 1micron or less), should go through the C-4 solder ball 130 (e.g., a 75micron diameter C-4 solder ball) in order to contact the circuit board115. In high bandwidth situations, it may impossible to get all of thevertical vias 125 out of one side. However, in this exemplary aspect ofthe present invention, C-4 solder balls 130 may be formed on both theupper and lower sides of the chip stack 110. In addition, these solderballs 130 may alternately contact adjacent vertical vias 125, which maycut at least in half the demand on either side for space in which toplace a C-4 solder ball 130, relieving a bandwidth bottleneck withoutadding latency arising from impedance of longer wires.

In particular, when the chip stack 110 includes high performance logicinstead of simply memory upon logic, it is essential to cool the chipstack 110 between the individual layers of the chip stack 110 duringoperation. Since there is no place for the heatsink in this design, thisexemplary aspect of the present invention provides another mechanism fordissipating heat.

In this exemplary aspect of the present invention, the chip stack 110may be efficiently cooled by etching channels 175 into the silicon ofeach layer of the chip stack 110. These channels 175 may conduct coolantfluids or gases throughout the chip between any two layers of the chipstack 110 to provide the necessary cooling.

The arrows in FIG. 1 a represent an exemplary flow of coolant in theassembly 100. In addition to the flow indicated by the arrows, as notedabove, the fluid may also flow between the layers of the chip stack 110and around the TWVs 123.

The cooling channels 175 may require a film thickness (e.g., a siliconfilm thickness) of at least 50 microns. However, assuming a 10:1 maximumaspect ratio for vertical vias, the vias may be as small as 5 microns indiameter, still at least a decade smaller than the C-4 solder balls 130needed to connect the vertical vias to the system board 120. Again inhigh density vertical via environments, it is still essential to relievethis bottleneck to bandwidth.

As noted above, an important aspect of the present invention is the twosided interleaving of C-4 solder balls 130 to the chip stack 110.

The present invention may also include connecting the two sides of thestack 110 to the circuit boards 115, and connecting the cooling channelsto the coolant fluid source.

As illustrated in the exemplary aspect of FIG. 1 a, a two-sidedpackaging interconnect to a chip stack may be used to achieve a moreefficient use of space on the system board 120. FIGS. 2-4 illustrateother exemplary aspects of the present invention. Many of the featuresof the aspects of FIGS. 2-4 are similar to those in FIG. 1 a, and thus,the description above with respect to FIG. 1 a is applicable withrespect to FIGS. 2-4 and will not be repeated.

For example, FIG. 2 illustrates another exemplary aspect of the presentinvention which may be used for chip identification personalization. Inthis exemplary aspect, the stack 110 may include identical chips (e.g.,chips having the same configuration of active elements). In this case,the vertical vias 123 may establish chip addresses.

On one side of the stack 110 may be connected to VDD, on the other sideof the stack 110 may be connected to GND. In this case, a vertical viano longer needs to penetrate the whole stack 110, but instead may onlycontact a portion on the chips in the stack 110 at that Z coordinatefrom one side of the stack 110. The other vias may be contacted with theopposite polarity from the same Z coordinate, but on the other side ofthe stack 110. The vertical via etch masks are the only layers that arepersonalized, but may be applied to identical processor chips.

For example, as illustrated in FIG. 2, circuit board 115 a is connectedto VDD and circuit board 115 b is connected to GND. Further, chips 110a-110 c are identical, and via 125 a is electrically connected to chips110 a and 110 b, but not to chip 110 c in the stack 110, whereas via 125b is electrically connected to chips 110 b and 110 c, but not to chip110 a in the stack 110.

FIG. 3 illustrates another exemplary aspect of the present inventionwhich may be used for multiple signal use of the same Z coordinate. Inthis exemplary aspect, the stack 110 may include heterogeneous chips(e.g., chips that are not identical). In this case, pads at a given Zcoordinate in the chip stack 110 may be used on different busses and/orfor different signals and uses. That is, the two-sided technique of thepresent invention provides for a means of using the same Z coordinatefor more than one signal or clock, power, or ground connection.

For example, as illustrated in FIG. 3, chips 110 a-110 c are notidentical, and circuit board 115 a is electrically connected to signalbus A, whereas circuit board 115 b is electrically connected to signalbus B.

FIG. 4 illustrates another exemplary aspect of the present inventionwhich is directed to a sensor application and/or emitter application.For example, a sensor such as an imaging sensor or RF-antenna which isexposed to the environment may be connected to a 3D chip stack. However,in this case, there would be no space for a conventional heat sink toattach to the chip stack. In the present invention, on the other hand,interlayer cooling enables the use one side of the package for true areaarray I/O and still allows the exposure of the sensor to theenvironment.

For example, as illustrated in FIG. 4, card 116 may include a surface116 a which is exposed to an environment such as the ambientenvironment. On the surface 116 a, a photosensor (e.g., a photodiode)may be formed for sensing or detecting light, or a light emittingelement may be formed for emitting light. Similarly, on the surface 116a, an RF-antenna may be formed for receiving or detecting an RF signal,or an RF emitter may be formed for emitting an RF signal. In this case,the circuit board 115 may be connected for example, to a system board toallow an I/O function for the stack 110.

FIG. 5 illustrates another possible implementation, according to anexemplary aspect of the present invention. Specifically, FIG. 5illustrates an assembly 500 which includes three chips 110 a-110 chaving an integrated circuit 150 formed thereon. The through-wafer vias(TWVs) 123 may be formed in heat transfer structures (e.g., pillars)which are etched into the silicon die 151 and form a fluid channel. Thechips 110 a-110 b may be embedded into a casing 112 (e.g., siliconcasing).

The casing 112 includes a coolant inlet 112 a and a coolant outlet 112b, through which a coolant fluid may be transported for cooling thestack 500. The casing 112 is bonded to circuit boards 115. That is, thechips 110 a-110 c may include a double sided C-4 I/O to circuit boards115. The electrical area array interconnects are realized with throughthe wafer vias 123.

FIG. 6 illustrates a cross-section of a through-wafer via 123, accordingto an exemplary aspect of the present invention. As illustrated in FIG.6, the chip 110 may include the integrated circuit 150 which includestransistor 155 and various wiring levels 157, and the silicon die 151formed on the integrated circuit 150. Further, a fluid channel 175 maybe formed between the chips in the chip stack 110 and between the chipstack 110 and the casing 112. The fluid channel 175 may be formedbetween the planar surface of the silicon die 151 and the have a heightwhich is less than about 50 microns.

As illustrated, in FIGS. 5 and 6, the heat transfer geometry accordingto the present invention may be structured into the silicon die 151 inthe form of pins and fins (e.g., the pillars of silicon in which thevias 123 are formed). The silicon die 151 of a chip in the stack 110 maybe bonded to a next upper layer with a solder layer 180.

For example, to bond the silicon die 151 of a chip to a next upperlayer, an “island” of an electrically conductive solder material (e.g.,a metal solder material) may be formed on the via 123 in a “pin” of thesilicon die 151. The island of solder material may then be surrounded bya ring structure (e.g., electrically insulative material) which sealsthe electrical interconnect from the fluid in the fluid channels. Thechip is then aligned with pressed to the next upper layer. Importantly,both bonding areas conduct heat to the fins (e.g., both the solder layer180 formed above and the solder layer 180 formed below a chip mayconduct heat away from the chip). The chip stack is then packaged into asilicon casing including the manifold and the electrical I/O's with thepossibility of ball grid array bonding on both sides of the package.

FIG. 7 illustrates an assembly 700 according to another exemplary aspectof the present invention. The assembly 700 is similar to assembly 500and includes through-wafer vias (TWVs) 123 formed in heat transferstructures (e.g., pillars) etched into the silicon die. However, asillustrated in FIG. 7, the assembly 700 may include only one singleactive IC layer 150 embedded into a silicon casing 112. This allowsdouble sided C-4 I/O to the circuit board 115. That is, the “chip stack”(e.g., as illustrated, for example, in FIG. 5) can be reduced to asingle chip with double sided I/O.

FIG. 8 illustrates an assembly 800 according to another exemplary aspectof the present invention. The assembly 800 is similar to assembly 500and includes through a stack 110, wafer vias (TWVs) 123 formed in heattransfer structures (e.g., pillars) etched into the silicon die 151, anda casing 112 which allows double side C-4 I/O to circuit boards 115.However, in the assembly 800, the chip stack 110 may include amulti-active IC layer 110 d, 110 e which include plural layers ofintegrated circuits which may be connected via TWVs. That is, an activelayer (e.g., an integrated circuit layer on an individual chip in thestack 110 in FIG. 1 a) can be replaced by multiple active layers asshown in FIG. 8. In this case, the uppermost layer of the multiplelayers may be etched to form the heat transfer structures (e.g.,pillars) of the silicon die, to provide for a coolant channel above themultiple layers.

FIG. 9 provides an isometric view of a cross-section of an assembly 900according to an exemplary aspect of the present invention. The assembly900 includes a stack 110 having chips 110 a-110 c which may include anintegrated circuit 150 and a silicon die 151. Further, the through-wafervias (TWVs) 123 are formed in heat transfer structures 124 (e.g.,pillars of silicon) etched into the silicon die 151, and a casing 112which allows double side C-4 I/O to circuit cards 115.

FIG. 10 illustrates a method 1000 of cooling a chip stack in an assembly(e.g., the assembly as illustrated in FIG. 1 a), according to anexemplary aspect of the present invention. The method 1000 includestransporting (1010) a coolant fluid to the chip stack through an inletformed in a casing, the casing including an integrated circuit which iselectrically connected to an integrated circuit of a chip in the chipstack by plural through wafer vias, transporting (1020) coolant fluid ina fluid channel formed between chips in the chip stack, and transporting(1030) coolant fluid from the chip stack through an outlet formed in acasing.

FIG. 11 illustrates a method 1100 of fabricating an assembly (e.g., theassembly as illustrated in FIG. 1 a), according to an exemplary aspectof the present invention. The method 1100 providing (1110) a chipincluding an integrated circuit, forming a casing including anintegrated circuit, an upper portion of the casing being formed on aside of the chip and a lower portion of the casing being formed onanother side of the chip, forming plural through-wafer vias (TWVs) forelectrically connecting the integrated circuit of the chip and theintegrated circuit of the casing, and connecting a card to the casingfor electrically connecting the casing to a system board.

FIGS. 12A-12C illustrate assemblies 1200, 1300 and 1400, respectively,according to other exemplary aspects of the present invention. Similarlyto the other exemplary aspects of the present invention, the assemblies1200, 1300 and 1400 may include a chip stack 1210, a daughtercard 1215 aand/or daughtercard 1215 b, lower casing 1212 TWVs 1223 and solder balls130.

In summary, the present invention may locally adapt the heat transferrate of a cold plate according to the power map with the goal tooptimize the overall heat removal rate for a given pumping power for alow gap 3D-IC stack with electrical interconnects. The present inventionmay alleviate problems with heat removal from hotspots and improve coldplate efficiency in terms of pumping power and removal of a maximumamount of energy with the least fluid volume. The present invention maywork for all types of cold plates but are especially efficient whereonly little vertical space is available like in interlayer cooling for3D packaged processors. In particular, the present invention may providefor a hot spot focused heat transfer architecture, a uniform junctiontemperature, and a multi-port (e.g., four port) fluid deliveryarchitecture to increase mass flow in constrained gaps.

With its unique and novel features, the exemplary aspects of the presentinvention may provide an assembly which may result in a more efficientuse of space on the system board than in conventional structures.

While the invention has been described in terms of one or moreembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims. Specifically, one of ordinary skill in the art willunderstand that the drawings herein are meant to be illustrative, andthe design of the inventive assembly is not limited to that disclosedherein but may be modified within the spirit and scope of the presentinvention.

Further, Applicant's intent is to encompass the equivalents of all claimelements, and no amendment to any claim in the present applicationshould be construed as a disclaimer of any interest in or right to anequivalent of any element or feature of the amended claim.

What is claimed is:
 1. A method of forming an assembly, said methodcomprising: providing a chip stack comprising a plurality of chips, thechips comprising integrated circuits formed thereon, the integratedcircuits comprising plural active elements; forming a casing,comprising: an upper portion on a side of said chip stack, said upperportion comprising an integrated circuit, the integrated circuitcomprising plural active elements; and a lower portion formed on anotherside of said chip stack, said lower portion comprising an integratedcircuit, the integrated circuit comprising plural active elements;etching a silicon layer formed on said integrated circuits of said chipsto form fluid channels in said chips in said chip stack; forming a firstplurality of through-wafer vias for interconnecting the chips in thechip stack; forming a second plurality of through-wafer vias forelectrically connecting said active elements of said integrated circuitsof said chips and said active elements of said integrated circuit ofsaid upper portion of said casing, and for electrically connecting saidactive elements of said integrated circuits of said chips and saidactive elements of said integrated circuit of said lower portion of saidcasing; providing a system board; and providing an upper card and alower card, wherein the upper card electrically connects said upperportion of said casing to the system board, and wherein the lower cardelectrically connects said lower portion of said casing to the systemboard.
 2. The method of claim 1, wherein said upper and lower cards areconnected to said upper and lower portions of said casing, respectively,by plural solder balls which are aligned with said second plurality ofthrough-wafer vias such that said second plurality of through-wafer viasare electrically connected to said upper and lower cards.
 3. Theassembly of claim 2, wherein at least one of said plurality of chipscomprises a silicon die formed on said integrated circuit of said chips,and wherein said first plurality of through-wafer vias being formed insilicon pillars of said silicon die.
 4. The method of claim 1, whereinsaid fluid channels are formed between an upper surface of a silicon dieformed on a first chip in said chip-stack, and a lower surface of asecond chip formed above said first chip in said chip-stack.
 5. Themethod of claim 4, wherein said upper and lower portions of said casingform a coolant inlet for transporting coolant into said chip-stack, anda coolant outlet for transporting said coolant out of said chip-stack.6. The method of claim 1, wherein said second plurality of through-wafervias comprise: first vias that electrically connect said integratedcircuit of a first chip of said plurality of chips to said upper casing;and second vias that electrically connect said integrated circuit of asecond chip of said plurality of chips to said lower casing.
 7. Themethod of claim 6, wherein said first and second vias are alternatelyformed such that an interleaving input/output (I/O) is formed above andbelow said chip-stack.